JP2006510258A - Maintaining linearity of power amplifier without isolator by dynamic adjustment of bias and power supply of active devices - Google Patents

Abstract

The amplifier circuit (100) comprises a drive stage (120) with at least one active device (140) for preamplification and output of the preamplified signal, and further amplification and amplification of the preamplified signal. And an output stage (160) with at least one active device (180) for output of the received signal. The detector (190) measures the level of the forward and reflected portions of the amplified signal, and the control circuit (145) substantially maintains the linearity of the amplifier circuit (100) during load variations, Modify the DC level or offset of the pre-amplified signal and / or the amplified signal. In addition, the control circuit (145) further maintains the linearity of the amplifier circuit (100) when the load changes, so that the drive stage and the output stage (120, 160) according to the levels of the forward signal and the reflected signal. DC bias is independently and selectively controlled and adjusted at the input of the active device (140, 180).

Description

  The present invention relates to a power amplifier circuit without an isolator that is typically used in a wireless communication device and maintains the linearity of the power amplifier under load variations. More specifically, linearity is maintained by dynamically adjusting the input and output bias of the active device of the power amplifier circuit.

  Power amplifiers are used in transmitters to amplify signals such as radio frequency (RF) signals. Such a power amplifier is included in a transmitter of a wireless communication device such as a mobile phone. A power amplifier typically provides an amplified RF signal to an antenna for air transmission.

  For example, an RF antenna applied to a mobile phone operates in a drastically changing environment, with the result that the antenna input impedance changes and a 4: 1 VSWR (voltage standing wave ratio) is rare. Especially at high power levels, this causes severe distortions in, for example, CDMA (code division multiple access), TDMA (time division multiple access), edges with non-fixed envelopes or W-CDMA modulated carrier signals.

  Traditional solutions to protect mobile phone power amplifiers from antenna mismatch conditions to maintain linearity are based on power amplifier and antenna configurations to limit the impact of load impedance variations on power amplifier performance. It is to use an isolator such as a circulator installed between the output load. The circulator ensures a proper 50 ohm load for the power amplifier under antenna mismatch conditions by extinguishing the power reflected at the isolator or third circulator port termination. The directivity of the power flow is made by a ferromagnetic material.

The above aspects of the prior art will be described in detail with reference to FIG. 1, which represents a basic block diagram of an arrangement 10 used for a power supply 12 that is isolated from a mismatched antenna 16 using a circulator 14. . The current source 18 and its impedance Z ₀ represent an ideal power supply (RF-transistor) 12. The matching circuit 20 is connected between the antenna 16 and the power supply 12, and another terminal 22 is grounded.

A part of the power P _{inc_circuc} from the matching circuit 20 to the circulator 14 is supplied to the antenna 16 as P _{inc_ant} , and a part of the power P _{refl_ant} is reflected by the antenna 16 and returned to the circulator 14. Since there is the circulator 14, the power P _{refl_ant} reflected from the antenna 16 is not reflected toward the source 12 and disappears at the circulator load P _diss . As a result, the power _{P Refl_source} that is reflected from the power _{P Refl_circ} and the matching circuit 20 towards reflected from the circulator 14 to the power supply 12 toward the power source 12 is zero. This avoids the extreme situation that occurs when incident and reflected waves are added in phase. However, it is desirable to maintain the linearity of the power amplifier and keep P _rad constant (under the control of the field strength display of the base station) to solve reflection losses that increase the signal voltage and current at the power supply 12. In addition, it is necessary to increase the incident power P _{inc_source} from the power source 12 and thereby increase the power _dissipation . Thus, the circulator 14 can only maintain part of the power amplifier linearity under antenna mismatch conditions. In addition, power dissipation and consumption remain high, thus requiring battery charging of the mobile phone, reducing battery life and at the same time reducing efficiency.

  It is desirable to remove the isolator or circulator 14 connected to the antenna 16. However, removal of the isolator allows load impedance variations to adversely affect power amplifier performance, eg, linearity. Accordingly, there is a need for a power amplifier that maintains the performance and linearity of the amplifier despite load impedance variations when the isolator is removed.

  In accordance with the present invention, the linear power output of the power amplifier is substantially maintained even when no isolator is connected to the load, despite load variations. This is achieved by dynamically adjusting the bias and feed of the active device in the power amplifier circuit without an isolator as a linearity correction scheme under certain load mismatch conditions. Thus, the linear output power is always kept constant for a given load delta throughout the dynamic range of operation without substantially reducing efficiency. More specifically, linearity is substantially constant despite load variations by independently and selectively adjusting the direct current (DC) bias at the input of the active device and the DC feed at the output of the active device. And the desired offset is given to the output signal.

  In one embodiment according to the present invention, an amplifier circuit is provided that maintains amplifier linearity. The amplifier circuit may be used, for example, in a wireless communication device. The amplifier circuit comprises a drive stage with at least one active device that performs preamplification and output of the preamplified signal, and an active device that performs further amplification of the preamplified signal and output of the amplified signal And an output stage. The detector measures the level of the forward and reflected portions of the amplified signal, and the control circuit maintains the pre-amplified signal and / or to substantially maintain the linearity of the amplifier circuit during load changes. Correct the DC level of the amplified signal. The control circuit further independent of the DC bias at the input of the active devices in the drive and output stages, depending on the levels of the forward and reflected signals, in order to substantially maintain the linearity of the amplifier circuit during load fluctuations. And selectively control and adjust.

  In another embodiment according to the present invention, a method is provided for substantially maintaining amplifier linearity under load variations. This method involves measuring the forward and reflected signal levels at the amplifier output and the difference between the measured forward and reflected signals to substantially maintain the linearity of the amplifier circuit during load changes. Or the output of at least one of the preamplified signal supplied from the drive stage of the amplifier circuit and the amplified signal supplied from the output stage of the amplifier circuit, depending on the measured level such as their ratio Modifying the DC level. This method provides independent DC bias at the input of the active device in the drive stage and / or output stage depending on the level of the forward and reflected signals in order to substantially maintain the linearity of the amplifier circuit during load variations. And further selectively adjusting.

  Further features and advantages of the present invention will become more readily apparent from consideration of the following description.

  The accompanying drawings identify and describe preferred embodiments of the present invention, wherein like elements are designated by like reference numerals throughout the drawings.

  The invention, together with attendant advantages, will be best understood by reference to the following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

  For example, an amplifier circuit for use in a wireless communication device is described, illustratively, an RF power amplifier is used in an RF antenna circuit. In the following description, various specific details, such as specific types and numbers of transistors, are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known circuits have not been described in detail in order not to unnecessarily obscure the present invention.

  The wireless communication device may be, for example, a mobile or cordless phone, pager, internet device, or other consumer device and is typically part of a communication system. FIG. 2 represents a wireless communication system such as a mobile phone system 40 comprising a main station or base station (BS) 50 and a plurality of sub-stations or mobile stations (MS) 60. Base station 50 includes a network controller 52, such as a computer, coupled to a transceiver 54, which is then coupled to a wireless transmission means such as an antenna 56. Connection means such as wire 58 couples controller 52 to the public or private network.

  Each mobile station 60 includes a processor 62 such as a microcontroller (μC) and / or a digital signal processor (DSP). Typically, the DSP processes the audio signal, while the μC manages the operation of the mobile station 60. The processor 62 is coupled to radio transmission means, for example transceiver means 64 coupled to an antenna 66. Memory 68, such as EPROM and RAM, is coupled to processor 62 and stores data regarding the operation and configuration of mobile station 60. Communication from the base station 50 to the mobile station 60 is performed on the downlink channel 72, while communication from the mobile station 60 to the base station 50 is performed on the uplink channel 74. The mobile station 60 also includes a user interface such as a keyboard and screen, and a microphone coupled to the transmission department or transmitter of the transceiver 64 and a speaker coupled to the receiver of the transceiver 64.

  The transmitter of the transceiver 64 transmits a signal via the uplink channel 74, and the receiver of the transceiver 64 receives the signal via the downlink channel 72. The transceiver 64 includes selection means for selectively coupling the power amplifier (PA) of the transmitter or the low noise amplifier (LNA) of the receiver to the antenna 66. As an example, the selection means includes a duplexer or bandpass filter that is tuned to transmit and receive the frequency range, respectively. As is well known in the art, the transceiver 64 also includes a downconverter and demodulator / decoder that converts the received radio frequency (RF) signal to an intermediate frequency and / or baseband signal. Other circuits are included in the receiver. In contrast, the transmitter section of the transceiver 64 includes an upconverter and a modulator / encoder. A converter that converts between analog and digital formats is also typically provided in the transceiver 64.

  FIG. 3 is a diagram illustrating an amplifier circuit 100 according to an embodiment of the present invention used as a power amplifier circuit to amplify an RF signal in a wireless communication device as an example. For example, the amplifier circuit 100 is part of the transceiver 64 of the mobile station 60 shown in FIG. Typically, the input of the amplifier circuit is coupled to a modulator and receives a modulated RF signal for amplification. The amplifier output is coupled to a load, such as an antenna 66, at which the amplified RF signal is transmitted over the air, for example, on the uplink channel 74.

  As shown in FIG. 3, the amplifier circuit 100 temporarily stores the input of the amplifier circuit 100 and matches its input impedance to a circuit coupled thereto, eg, the output impedance of the modulator. 110. The output of input matching circuit 110 is coupled to drive stage 120 via at least one DC blocking capacitor 130. A signal to be amplified, such as a modulated signal, is provided to capacitor 130 by input matching circuit 110, which subsequently blocks the DC component and provides a signal substantially free of DC offset to drive stage 120. Supply.

  Drive stage 120 includes at least one active device, such as transistor 140, which receives a substantially DC free signal from capacitor 130 and preamplifies it to a first level. As an example, the preamplifier transistor is a bipolar transistor such as NPN transistor 140 having a base 142 coupled to capacitor 130. Base 142 is also coupled to a bias control circuit 145 that provides an appropriate DC bias signal. This allows the bias control circuit 145 to control the DC bias at the input of the transistor 140, for example to adjust it. The emitter of transistor 140 is coupled to ground, while the output or collector 147 of transistor 140 is an intermediate stage matching circuit used for buffering and impedance matching between the input of drive stage 120 and output stage 160. 150.

  The pre-amplified signal from the drive stage 120 passes through an intermediate stage matching circuit 150 and at least one DC blocking capacitor 170 that substantially blocks the DC signal as well as the DC blocking capacitor 130. Supplied to the input.

  Output stage 160 is similar to drive stage 120 and further includes at least one transistor 180 that receives a signal substantially free of DC from capacitor 170 and amplifies it to an output level. As an example, output transistor 180 is a bipolar transistor such as an NPN transistor having a base 182 coupled to capacitor 170. The base 182 of the output transistor 180 is also coupled to a bias control circuit 145 to provide an appropriate DC bias signal to the output transistor 180. The emitter of transistor 180 is coupled to ground, while the output or collector 187 of transistor 180 is coupled directly or indirectly to the load without an isolator. Further, the emitter region of each active device 140, 180 is selected for optimal performance for a given load, intermediate stage and power supply conditions.

  In addition, the output or collector 147, 187 of each transistor 140, 180 is also independently coupled to a bias control circuit 145. This is because the bias control circuit 145 independently and selectively selects the DC level or offset of the preamplified signal at the output 147 of the transistor 140 and / or the DC level or offset of the amplified signal at the output 187 of the transistor 180. Can be changed to Further, by independently coupling each input / control port, eg, the bases 142, 182 of the transistors 140, 180, to the bias control circuit 145, the bias control circuit 145 independently and independently adjusts the DC bias at the inputs of the transistors 140, 180. It can be selectively controlled, for example, it can be independently and selectively adjusted, and thus the amplification or gain of the drive and output stages 120, 160 can be modified.

  As an example, consider the case where the power amplifier supplies 30 dBm output power to a 50 ohm load. If the output of the last stage of the power amplifier has a peak voltage amplitude of 1.4 volts for linear operation, the lossless impedance matching network separating the load and power amplifier should have an impedance conversion ratio of 51: 1. There is.

  Assume worst case mismatch conditions for the entire phase of a constant VSWR. The extremes of impedance are high load and low load. In the former case, high voltage amplitude appears across the output of the final stage, causing non-linearity in the form of clipping due to the beginning of high AC impedance. In the latter case, the demand for output current increases due to the onset of low AC impedance. By monitoring the incident power level and the reflected power level, a measurement of the impedance condition is obtained as shown in block 200 of FIG. Next, at block 210, the impedance level or mismatch is checked and if a normal or matching level is obtained, normal matching operation is continued at block 220. If the impedance level is not normal, i.e. mismatched, the difference or ratio between the measured forward and reflected signals is large, indicating that the forward signal is relatively large, or that the difference or ratio is It is determined at block 230 whether the forward signal is small and is relatively small. Next, in blocks 240 and 250, the DC bias at both the input and output of each of the driver and output transistors is either in one direction or the other depending on whether the ratio measured in block 230 is large or small. It is adjusted independently and selectively in the direction. The impedance condition is then re-measured back to block 200 and these operations are repeated until a matching level is obtained at block 210 and normal matching operations continue at block 220. The monitoring and measurement of impedance in block 200 is inspected continuously or intermittently and adjustments are made as necessary to reach the matching conditions of block 220.

  Referring to FIG. 3, a detector, such as power detector 190, is also coupled to output 187 of transistor 180 to detect the level of the amplified RF signal at the output of output stage 160, eg, the power level. The power detector 190 is then coupled to the bias control circuit 145. The output 195 of the amplifier circuit 100 is coupled to the antenna without an isolator.

  The power detector 190 supplies the DC bias control circuit 145 with measured amounts of forward power and reflected output power of the amplifier circuit 100. Depending on the forward power level and the reflected power level, the DC bias control circuit 145 pre-amplifies at the output 147 of the drive stage transistor 140 to substantially maintain a certain linearity of the amplifier circuit 100 during load changes. The DC level of the amplified signal and / or the DC level of the signal amplified at the output 187 of the output stage transistor 180 are independently and selectively changed. The control circuit 145 is responsive to the forward and reflected signals to maintain the linearity of the amplifier circuit 100 substantially constant regardless of the impedance variation of the load coupled to the output 195 of the amplifier circuit 100. , Further independently and selectively control and adjust the DC bias at the inputs 142, 182 of the active devices 140, 180 of the drive stage 120 and output stage 160.

  In particular, the bias control circuit 145 determines the respective inputs of the driver transistor 140 and the output transistor 160, eg, the bases 142, 182, and the respective outputs, eg, the collector, depending on the difference between the forward power level and the reflected power level. DC bias is adjusted independently and selectively at both 147 and 187. As a result, the linearity output power is substantially maintained regardless of load fluctuations without significantly changing the output stage of the power amplifier circuit.

To illustrate one solution, the optimal actual impedance of the collector is proportional to the ratio of the collector power supply voltage squared to the output power, and is R _opt ~ V _CC ² / (2 × P _out ). . Thus, changes in load impedance are accommodated by changes in R _opt and input bias according to the required P _out and linearity.

  As is well known to those skilled in the art, changes in forward and reflected power levels measured by power detector 190 are related to changes in load impedance, for example, the impedance of antenna 66 shown in FIG. It is done. In particular, for load impedances that are substantially matched to the output impedance of the output of the amplifier circuit 100, the ratio or difference between the forward power level and the reflected power level is large, while for impedances that are not substantially matched. The ratio or difference is small. US Pat. No. 5,423,082, which is incorporated herein by reference in its entirety, compensates for a variable antenna load without an isolator by adjusting the gain of the variable gain stage. A transmitter is disclosed that includes closed loop feedback achieved in view of reflected output energy to maintain loop gain.

  Bias control circuits such as those disclosed in US Pat. Nos. 5,442,322 and 5,712,593, the entire contents of which are incorporated herein by reference, are also well known in the art. In U.S. Pat. No. 5,442,322, the bias control circuit compares the bias control voltage with a value representing the current in the active device and applies a control signal to the control terminal of the active device to control the operating point of the active device. Supply. The bias point of the power amplifier is similarly controlled by the control circuit in US Pat. No. 5,712,593 according to the result of comparing the reference value with the filtered portion of the RF output signal. Changing the amplifier bias point limits the effect of load impedance variations on amplifier performance. US Pat. No. 6,064,266, which is hereby incorporated by reference in its entirety, similarly relates to limiting the effect of load impedance variation on amplifier performance, and this limitation is This is accomplished by changing the RF output signal path rather than the DC bias by switching to a resistor that is in parallel with the output impedance when a load impedance variation above a predetermined value is detected.

  The bias control circuit 145 of the amplifier circuit 100 includes a processor or comparator that compares the forward power level and the reflected power level measured by the power detector 190 with at least one threshold. Based on this comparison, the DC bias control circuit 145 may need to maintain the linearity of the amplifier circuit 100 during load changes as substantially constant, i.e., at the level of the forward and reflected signals. In response, the DC level or offset of the pre-amplified and / or amplified signal provided by the drive stage and output stage transistors 140, 180 is changed. The bias control circuit 145 further includes transistors 140 and 180 in the drive stage and the output stage according to the levels of the forward signal and the reflected signal in order to maintain the linearity of the amplifier circuit at the time of load variation substantially constant. The DC bias at the input of each is controlled and adjusted independently and selectively.

  FIG. 5 depicts a flowchart 300 of a method for maintaining the performance of an isolator-less amplifier circuit according to the present invention. In block 310, the power detector measures the forward and reflected power levels at the output of the amplifier circuit and provides this information to the bias control circuit 145. Depending on the measured forward power level and the reflected power level, for example, depending on the value of these differences or ratios, at block 320, the control circuit 145 substantially reduces the linearity of the amplifier circuit 100 during load changes. Pre-amplified and / or amplified signals supplied by the drive stage and output stage transistors 140, 180 as needed, ie, depending on the level of the forward and reflected signals. Selectively and independently change the DC level or offset. The bias control circuit 145 further includes transistors 140 and 140 in the drive stage and the output stage in accordance with the levels of the forward signal and the reflected signal in order to maintain the linearity of the amplifier circuit 100 during a load change substantially constant. With 180 inputs, the DC bias is independently and selectively controlled and adjusted.

  Although the invention has been described in particular detail with reference to specific exemplary embodiments thereof, various modifications and changes can be made from the broader intended spirit and scope of the invention as set forth in the claims. It should also be appreciated that it can be added to those embodiments without doing so. The specification and drawings are accordingly to be regarded in an illustrative manner and are not intended to limit the scope of the matters recited in the claims.

1 is a block diagram of a prior art power source that is insulated from a mismatched antenna using a circulator. FIG. 1 represents a wireless communication system according to the present invention. FIG. 3 represents an amplifier circuit without an isolator according to the invention. 4 is a flowchart of a method for maintaining performance, eg, linearity, of an isolator-less amplifier circuit according to the present invention. 2 is a summarized flowchart of a method for maintaining the performance, eg, linearity, of an amplifier circuit without an isolator according to the present invention.

Claims (20)

A drive stage having at least one first active device that receives a signal for preamplification and outputs a preamplified signal;
An output stage having at least one second active device that receives the pre-amplified signal for further amplification and outputs the amplified signal;
A detector for measuring a forward signal level and a reflected signal level of the amplified signal;
In order to substantially maintain the linearity of the amplifier circuit when the load fluctuates, at least one of the pre-amplified signal and the amplified signal according to the level of the forward signal and the level of the reflected signal An amplifier circuit comprising a control circuit for changing one of the DC levels.   The control circuit changes DC levels of both the pre-amplified signal and the amplified signal in order to substantially maintain the linearity of the amplifier circuit when the load changes. The amplifier circuit according to claim 1.   2. The amplifier circuit according to claim 1, wherein the output stage is coupled to a load without interposing an isolation device between the output stage and the load.   The control circuit includes the at least one first active device in response to the level of the forward signal and the level of the reflected signal to substantially maintain the linearity of the amplifier circuit during the load change and The amplifier circuit of claim 1, further adjusting a gain of the at least one second active device.   5. The amplifier circuit of claim 4, wherein the output stage is coupled to a load without interposing an isolation device between the output stage and the load.   The amplifier circuit according to claim 4, wherein the control circuit independently adjusts the gain of each of the first active device and the second active device.   The amplifier circuit according to claim 4, wherein at least one of the first active device and the second active device is an NPN transistor.   The amplifier circuit according to claim 4, wherein the first active device and the second active device are NPN transistors.   An input matching circuit coupled between the input of the amplifier circuit and the drive stage and further matching an input impedance of the amplifier circuit to an output impedance of a device coupled to the input. 2. The amplifier circuit according to 1.   The amplifier circuit of claim 9, further comprising at least one capacitor coupled between the input matching circuit and the driving stage.   The amplifier circuit of claim 1, further comprising at least one capacitor coupled between an input of the amplifier circuit and the drive stage.   2. An intermediate stage matching circuit coupled between the output of the drive stage and the input of the output stage and further matching an input impedance of the output stage with an output impedance of the drive stage. An amplifier circuit according to 1.   The amplifier circuit of claim 10, further comprising at least one capacitor coupled between the intermediate stage matching circuit and the output stage.   2. The amplifier circuit of claim 1, further comprising at least one capacitor coupled between the intermediate stage matching circuit and the output stage. A drive stage having at least one first active device that receives a signal for preamplification and outputs a preamplified signal;
An output stage having at least one second active device that receives the pre-amplified signal for further amplification and outputs the amplified signal;
A detector for measuring a forward signal level and a reflected signal level of the amplified signal;
In order to substantially maintain the linearity of the amplifier circuit when the load fluctuates, at least one of the pre-amplified signal and the amplified signal according to the level of the forward signal and the level of the reflected signal A wireless communication apparatus having an amplifier circuit including a control circuit for changing one DC level.   The control circuit changes DC levels of both the pre-amplified signal and the amplified signal in order to substantially maintain the linearity of the amplifier circuit when the load changes. The wireless communication apparatus according to claim 15.   16. The wireless communication device of claim 15, wherein the output stage is coupled to a load without interposing an isolation device between the output stage and the load.   The control circuit includes the at least one first active device in response to the level of the forward signal and the level of the reflected signal to substantially maintain the linearity of the amplifier circuit during the load change and 16. The wireless communication apparatus of claim 15, further controlling on / off switching of the at least one second active device. A method of substantially maintaining the linearity of the amplifier circuit during a change in load coupled to the output of the amplifier circuit, comprising:
Measuring the level of the forward signal and the level of the reflected signal at the output;
In order to substantially maintain the linearity of the amplifier circuit when the load fluctuates, the pre-amplified signal supplied from the driving stage of the amplifier circuit according to the level of the forward signal and the level of the reflected signal, and the Changing the DC level of at least one of the amplified signals supplied from the output stage of the amplifier circuit.   20. The method of claim 19, further comprising: independently switching on and off a first active device of the drive stage and a second active device of the output stage in response to the power level. .

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